Resistance element for pyrometers



April 17, 1951 u. LAMM 2,549,2ll

RESISTANCE ELEMENT FOR PXBMETERS Filed Aug. 21, 1947 /m nfor U Lamm LOM 52/ %Var/79% Patented Apr. 17, 1951 7 UNITED STATES ATENT-j OFFICE i 2,549,2r1 A L I i' RES'STANCE LEMENT ron rYRoME rERs Uno Lamm, Ludvika, %we den, assignor'to Allmma Svenska' Elektriska Aktiebol'aget; Vase tetas', Sweden, a Swedish corp'orati'on' Application August 21, 1947,. SerialvNo. 769943. In SwedenAugust 2 1, 1942 6 Claims. (CI. 201457) Pyrometers for continuous measuring of high temperatures, especially for regulating purposes, often consist of electric resistance elements forming part of a bridge connection or the like. In orderto present an exactly reliable temperature coeflicient, such resistance elements should consist of pure metals, for practical reasons enerally in the form of wire. However, even the most heat resistant of the pure metals, as platinum and its homologues osmium and iridium, are sensitive at high temperatures to certain common impurities of the air, especially carbon monoxide and dioxide. For this reason, resistance elements for pyrometers have been made of' platinum wire embedded in glass or quartz. However, glass becomes too soft at high temperatures and at the same time rather highly electrically conductive, and quartz attacks platinum under similar conditions. For these reasons, pyrometer of this kind could not be employed above temperatures of about 500" C.

It has now been found that reliable resistance element for pyrometers up to 1000 C. can be obtained by enclosing a metal wire in porcelain, steatite or similar ceramic material in an airtight manner. such materials still retain their shape up to 1500` C. and thereby eiciently protect the wire. If such qualities are chosen which are employed for high class electric insulators, the conductivity even at high temperatures does not become so high as to influence appreciably the result of the resistance measuring. The same applies to the glaze qualities generally used for such porcelain. The glaze which can be used for a resistance element for 1000 cshould still be highly viscous at 1400 C. For this purpose, the molecular proportion between SiOz and basic oxides should be at least 5, and the latter should also contain magnesia. such a glaze does not attack the platinum wire.

As a suitable example of the construction of such a resistance element the following may 'fractory metal alloy, for instance chromiumnickel-iron, said tube being preferably suficiently long to reach through the furnace wall and into the furnace with a length corresponding to that of the resistance helix. At the other end, the metal tube is preferably combined with a space containin a connection plate. The conductors inside said metal tube may be insulated by surrounding porcelain or steatite beads.

A platinum wire of the aforesaid diameter and of 1 to 2 meter length, formin part of a dierential connection, as of a Wheatstone bridge, has been found sufiicient for creating a regulating power which can be amplifiecl by means of transductors (D. C. saturable inductances).

I claim as my invention:

1. A resistance element for pyrometers, comprising a .porcelain core, a wireof a metal having a high melting point and low Chemical afiinity wound on said core, a porcelain tube' tightly surrounding said core and wire, and a glaze having a high point of fusion filling the space between said core and tube and the interstices between the windings of said wire and gas-tightly enclosing said wire.

serve, which is illustrated in the accompanying 2. A resistance element for pyrometers, comprisin a porcelain core, a platinum wire wound on said core, a porcelain tube tightly surrounding said core and wire, and a glaze having a high point of fusion filling the space between said core and tube and the interstices between the windings of said wire and gas-tightly enclosing said wire.

3. 'A' resistance element for pyrometers, comprising a slightly tapered porcelain core having a helical groove therein, a wire of a metal having a high melting point and low Chemical affinity wound in said groove, a porcelain tube having a slightly tapered hollow space tightly surroundr ing said core and wire, and a glaze having a high point-of fusion filling the space between said core and tube and the interstices :between the windings of said wire and gas-tightly enclosin said wire.

4. A resistance element for pyrometers, comprising a. porcelain core, a wire of a. metal having a high meltng point and low Chemical affinity wound on said core, a, porcelain tube tightly surroundin said core and wire, and& glaze of a composition which is still highly viscous at 1400 C. filling the space between said core and. tube and the interstices between the windings of' said wire and gas-tightly enclosing said wre.

5. A resistance element as claimed in claim (1 comprising also leading-in wires of considerably larger diameter than the wire wound on the porcelain core.

6. A resistance element as claimed in claim 1 comprising also a. tube of a chromium-iron alloy surrounding said porcelain tube and leading-in conductors.

UNO LAMM.

` 4 REFERENCES CITED UNITED STATES PATENTS Number Number Name Date Hensley et al. Nov. 25, 1890 Abbott Aug. 24, 1920 Hubbard et al Nov. 1, 1938 Randolph Feb. 25, 1941 Hall Feb. 3, 1942 FOREIGN PATENTS Country Date Great Britain Nov. 2, 1939 

1. A RESISTANCE ELEMENT FOR PYROMETERS, COMPRISING A PORCELAIN CORE, A WIRE OF A METAL HAVING A HIGH MELTING POINT AND LOW CHEMICAL AFFINITY WOUND ON SAID CORE, A PORCELAIN TUBE TIGHTLY SURROUNDING SAID CORE AND WIRE, AND A GLAZE HAVING A HIGH POINT OF FUSION FULLING THE SPACE BETWEEN SAID CORE AND TUBE AND THE INTERSTICES BETWEEN THE WINDINGS OF SAID WIRE AND GAS-TIGHTLY ENCLOSING SAID WIRE. 